The invention relates to an exhaust system for internal combustion engines, preferably for motorcycles, having an exhaust tract that has at least one first flow path and a second flow path for an exhaust gas stream, wherein the first and the second flow path extend fluidically separated from each other from a pre-silencer to an end silencer.
More and more severe legal restrictions are being imposed on the noise generated by motorcycles. The noise level of a motorcycle is tested at standstill as well during a drive-by test as the motorcycle accelerates. High-powered motorcycles in particular are subject to the problem that the exhaust gas flow must be severely restricted to stay under the legal noise limit, which leads to a significant reduction in performance and an undesired restriction of the engine torque.
In order to obtain high performance at high speeds and a simultaneously reduced noise level at low speeds, exhaust systems known from prior art have a flap arranged in the flow path, which limits the exhaust gas stream as a function of speed. With this method, however, it is a disadvantage that at all times, the entire exhaust gas stream is affected and the flow experiences strong turbulence when the flap is partially open, which has a negative impact on the torque curve. Also, to achieve future noise level limits, the exhaust gas stream has to be limited in the speed range of the noise level measurement to such an extent that the desired performance would no longer be achieved.
Given this background, the object of the invention is to provide an exhaust system for high-performance motorcycles, the acoustics of which meets the legal requirements and which simultaneously delivers the desired power and torque curve across the entire speed range.
These and other objects are achieved by an exhaust system for internal combustion engines having an exhaust tract which has at least one first flow path and one second flow path for an exhaust gas stream. The first and second flow paths extend fluidically separated from each other from a pre-silencer to at least one end silencer. The first flow path is continually closable by a controllable flap as a function of speed, with the exhaust gas stream flowing through the second flow path when the flap is closed.
According to the invention, it is therefore provided to provide two flow paths for the exhaust gas stream, wherein, as a function of speed, exhaust gas flows through one or the other, and/or in part also through both. At low engine speeds, such as less than 5,000 rpm, for example, the flap is closed in the first flow path so that the exhaust gas stream flows from the pre-silencer via the second flow path to the end silencer without being hindered by a flap and at an optimal flow. In doing so, a flow-through mass and a flow-through speed of the exhaust gas are reached which ensure sufficient power and sufficient torque in the lower speed range. At the same time, the noise developed is sufficiently low to satisfy the legal requirements.
As the speed continues to increase, the flap continues to open so that the exhaust gas flows from the pre-silencer also through the first flow path. At high speeds and high power output, the flap is completely open and the exhaust gas stream flows essentially through the first flow path. A small part additionally flows through the second flow path. It is possible to influence the noise development directly by controlling the flap, wherein unlimited flow through the second flow path is provided at all times. It is therefore possible to divide the flow paths into an acoustically optimized path at low speeds and a power-optimized path for high speeds.
One embodiment of the invention provides that a flow diameter area of the first flow path, which is designed for high performance, is larger than a flow diameter area of the second flow path.
In a further embodiment of the invention, the first and second flow paths extend between pre- and end silencers, separate from each other and arranged side-by-side. In a further embodiment of the invention, the first and second flow paths extend coaxially in one another, with the second flow path surrounding the first flow path in a spaced apart fashion and the space between the first and second flow path forming the flow diameter area of the second flow path. The flow paths are generally formed by pipes so that the first flow path can be realized as an internal pipe within a larger external pipe (second flow path). The space between the external wall of the internal pipe and the internal wall of the external pipe determines the flow diameter area of the second flow path. The inner diameter of the internal pipe determines the flow diameter area of the first flow path. In an embodiment where flow paths are separated from each other and arranged side-by-side, appropriate pipes can be installed side-by-side, preferably in parallel.
The exhaust system includes the end silencer into which the first and second flow paths extend, wherein in one embodiment of the invention, the first flow path completely penetrates the end silencer in the direction of flow up to its outlet. The exhaust gas path therefore extends in the high-speed range directly through the first flow path to the outlet.
In an advantageous embodiment of the invention, it is provided that the second flow path ends in the end silencer in a chamber, which provides an instantly enlarged flow diameter area compared to the second flow path. The enlarged flow diameter area is realized, for example, by a large-volume chamber in the end silencer, through which the exhaust gas of the second flow path flows. In the case of the embodiment having an internal pipe in the external pipe, the internal pipe (first flow path) extends to the outlet and is surrounded by the volume of the end silencer, which clearly increases relative to the external pipe (second flow path). In the embodiment with flow paths arranged side-by-side, an area is provided in the end silencer next to the first flow path, which provides the volume enlargement in the form of a chamber.
In an economical embodiment of the invention, the exhaust system according to the invention is characterized in that the first flow path is fluidically connected to the chamber in the end silencer. In a preferred embodiment, this can be achieved in that the first flow path is perforated or developed with slots within the end silencer. When using a pipe as the first flow path, for example, the external wall area is provided with a multitude of holes or slots so that the exhaust gas can flow from the chamber in the end silencer into the first flow path and from there out of the outlet. The holes or slots are provided in an embodiment of the invention over the entire surrounding area so that in the end silencer, exhaust gas can flow into the pipe forming the first flow path over a length designed for the effectiveness.
In an embodiment of the invention, it is furthermore provided that the end silencer is divided by a separating element in the direction of flow, for example a wall element, wherein the chamber is provided in an upstream first section, and an insulator is provided in a downstream second section adjacent to the outlet. The insulator surrounds the first flow path. The insulation of the area adjacent to the outlet allows for a further shielding and defined reduction of the noise development. The noise development can be influenced once more with the size of the first and second section, with a favorable division being that, in a specific embodiment, the first section is two thirds and the second section is one third of the total length of the end silencer. A suitable insulator is conventional insulation wool.
Furthermore, the invention includes an exhaust system in which the two flow paths extend from the pre-silencer to two separate end silencers in the direction of the flow and one of the two flow paths can be closed and/or throttled by the flap.
The invention furthermore protects a motorcycle having an exhaust system that has a random combination of the characteristics represented above to the extent this is technically possible.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.
In all views, identical reference symbols refer to identical parts.